Hollow Coral-like Black g-C3N4 Nanoparticles for Photothermal-Assisted Photocatalytic Hydrogen Generation

Abstract

Graphitic carbon nitride (g-C₃N₄) is a promising photocatalyst for energy and environmental applications due to its stability and intrinsic activity, but it suffers from limited visible-light absorption and poor light harvesting. Herein, a porous, highly crystalline black g-C₃N₄ (H-BCN) was synthesized via a facile one-step molten salt calcination strategy. This material exhibits significantly enhanced light absorption and a pronounced photothermal effect, greatly boosting photocatalytic H₂ production. The optimal H-BCN achieved a H₂ evolution rate of 12.71 mmol g⁻¹ h⁻¹ under the full-spectrum illumination of a 300 W Xenon lamp, which is 1.94 times that of pristine yellow g-C₃N₄ (YCN) and exhibited a quantum efficiency (AQE) of 9.4% at 420 nm in water. The enhanced performance stems from four key factors: (i) laver-derived biomass carbon incorporated during calcination produces black g-C₃N₄ with improved photon harvesting and photothermal conversion; (ii) coral-like porous cavities promote multiple internal reflections of light, increasing absorption efficiency; (iii) molten salt synthesis raises crystallinity and introduces K/Na intercalation between layers, creating doping channels that accelerate charge transport; and (iv) surface functional groups on biochar improve hydrophilicity, facilitating catalyst−water interaction. This work provides a rational design strategy for developing black g-C₃N₄ photocatalysts with superior light absorption and photothermal-assisted photocatalytic hydrogen generation.